Prior electronic module assemblies are known in which a polyimide flexible circuit board substrate has been mounted to a rigidizer plate and the rigidizer plate is then bent such that the plate forms part of an exterior housing for an electronic module assembly which includes the flexible substrate. Examples of such prior art structures are shown in U.S. Pat. Nos. 5,103,375, 5,159,751, 5,216,581, 5,265,322 and 5,170,326 all assigned to the same assignee as the present invention. Such assemblies generally contemplate the use of an integral mandrel or a removable mandrel to implement bending the rigidizer plate of the flexible circuit board assembly around one or more bend axes. In such assemblies, generally an intermediate portion of the flexible substrate is left unbonded or unmounted to the underlying rigidizer plate to prevent excessive stressing of the flexible substrate during the bending process and/or rupturing of conductive interconnect paths on the flexible substrate during the bend process. However, it has been determined that by having such an unbonded intermediate portion of the flexible substrate, the flexible substrate may bend in an undesirable manner during the bending process creating creasing of the flexible substrate or areas of potential high stress. This may result in rupturing conductive interconnect paths of the flexible substrate immediately or during thermal cycling. What is therefore desired is an improved flexible circuit board assembly and method which avoids implementing undesired bends for the flexible substrate during the bending process.